You need an alignment when you notice:
Many vehicles today are equipped with rear suspensions that can be adjusted for alignment. If this is the case, your vehicle may need a "front end" alignment or a "four wheel" alignment, depending on the symptoms you are experiencing. See your local Michelin authorized tire dealer for service and inspection.
Take air out of your tire, using a tire pressure gauge, until your air pressure reading matches your vehicle manufacturer’s recommended psi. To find the proper air pressure, consult your vehicle’s owner’s manual or find your recommended psi on the sticker on your door jam. (Here’s how.)